The present invention relates in general to fiber optic technology and more particularly to a fiber optic transmission system in a metropolitan area network.
In conventional fiber optic transmission systems, Raman amplification is associated with long haul, for example, greater than 500 km, and ultra long haul, for example, greater than 3000 km, transport. In metropolitan area networks spanning distances of, for example, less than 300 km, there is a necessity to support a broad spectrum of services and data rates in the metropolitan environment while keeping the costs as low as possible. Apparently because of a perceived large expense involved with the use of Raman amplification, conventional metropolitan optical transmission systems have avoided the use of Raman amplifiers. Instead, Raman amplifiers have been viewed as useful only to extend transmission distances far beyond those used in typical metropolitan systems.
From the foregoing, it may be appreciated by those skilled in the art that a need has arisen for a technique to compensate for losses introduced into a metropolitan fiber optic transmission environment. In accordance with the present invention, a fiber optic transmission system in a metropolitan area network is provided that substantially eliminates or greatly reduces disadvantages and problems associated with conventional metropolitan fiber optic implementations.
In one embodiment, a fiber optic transmission system for a metropolitan area network comprises a plurality of interface devices operable to be coupled to a fiber optic transmission link carrying an optical signal and having a length of 300 km or less. The link has a transmission loss associated with an unpumped state of the link, and the plurality of interface devices collectively introduce a loss of at least 6 decibels to the link. The system also comprises a distributed Raman amplifier stage coupled to the link, the distributed Raman amplifier stage operable to pump at least a portion of the link to reduce the transmission loss of the at least a portion of the link compared to its unpumped state, the reduced link transmission loss facilitating allocation of at least a portion of a gain to at least partially offset the loss associated with the plurality of interface devices.
In another embodiment, a fiber optic transmission system for a metropolitan area network comprises a transmitter assembly operable to generate a plurality of optical wavelength signals. The system also comprises a combiner operable to combine the plurality of optical wavelength signals into a multiple wavelength optical signal comprising at least 160 wavelengths and occupying a bandwidth of at least 60 nanometers. The combiner is operable to facilitate communication of the multiple wavelength optical signal over a communication link in a metropolitan area network spanning no more than 300 kilometers. The system further comprises a multiple stage optical amplifier coupled to the communication link and comprising at least one Raman amplifier stage capable of operating on a bandwidth of at least 60 nanometers.
In still another embodiment, a fiber optic transmission system for a metropolitan area network comprises a transmitter assembly operable to generate a plurality of optical wavelength signals. Each of the plurality of optical wavelength signals comprises a transport rate of at least 9.5 gigabits per second. The system also comprises a combiner operable to combine the plurality of optical wavelength signals into a multiple wavelength optical signal and to facilitate communication of the multiple wavelength optical signal over a communication link in a metropolitan area network spanning no more than 300 kilometers. The system further comprises a discrete Raman amplifier stage comprising a gain medium. At least a portion of the gain medium comprises a dispersion compensating fiber operable to at least partially compensate for a dispersion in at least some of the plurality of optical wavelength signals. The discrete Raman amplifier stage is operable to pump the dispersion compensating fiber to produce Raman gain to at least partially offset a loss associated with the dispersion compensating fiber.
In another embodiment, an optical communication system comprises a communication link in a metropolitan area network spanning no more than 300 kilometers. The communication link is operable to communicate a multiple wavelength optical signal comprising at least 160 wavelengths and occupying a bandwidth of at least 60 nanometers. At least some wavelengths are dedicated for communication with particular nodes coupled to the communication link. The system also comprises a multiple stage optical amplifier coupled to the communication link and comprising at least one Raman amplifier stage capable of operating on a bandwidth of at least 60 nanometers.
A method embodiment comprises communicating a plurality of optical signals over a communication link in a metropolitan area network spanning 300 kilometers or less, wherein the communication link comprises a transmission loss associated with an unpumped state. The method further comprises passing at least some of the plurality of optical signals through a plurality of interface devices coupled to the communication link, wherein the plurality of interface devices collectively introduce a loss of at least 6 decibels to the communication link. The method still further comprises forming a distributed Raman amplification stage by pumping at least a portion of the communication link to reduce the transmission loss of the at least a portion of the link compared to its unpumped state, the reduced link transmission loss facilitating allocation of at least a portion of a gain to at least partially offset the loss associated with the plurality of interface devices.
In another method embodiment, a method of communicating optical signals in a metropolitan area network comprises generating a plurality of optical wavelength signals and combining at least some of the plurality of wavelength signals into a multiple wavelength optical signal comprising at least 160 wavelengths and occupying a bandwidth of at least 60 nanometers. The method also comprises communicating the multiple wavelength optical signal over a communication link in a metropolitan area network spanning no more than 300 kilometers, and passing at least most of the plurality of wavelengths through a multiple stage optical amplifier capable of operating on a bandwidth of at least 60 nanometers. The multiple stage optical amplifier offsets at least a portion of a loss experienced by the multiple wavelength optical signal as it traverses the communication link.
In still another method embodiment, a method of communicating optical signals in a metropolitan area network comprises generating a plurality of optical wavelength signals, each of the plurality of optical wavelength signals comprising a transport rate of at least 9.5 gigabits per second. The method also comprises combining at least some of the plurality of wavelength signals into a multiple wavelength optical signal, and communicating the multiple wavelength optical signal over a communication link in a metropolitan area network spanning no more than 300 kilometers. The method further comprises passing the multiple wavelength optical signal over a dispersion compensating fiber to at least partially compensate for a dispersion experienced by at least a portion of the multiple wavelength optical signal. In addition, the method comprises pumping the dispersion compensating fiber to produce Raman gain to at least partially offset a loss associated with the dispersion compensating fiber.
Various embodiments of the present invention provide various technical advantages. For example, one aspect of this disclosure envisions metropolitan systems utilizing large numbers of channels and large numbers of interface devices to accommodate routing and processing of varying traffic patterns through the network. These interface devices can, in some cases, be quite lossy. One aspect of this disclosure proposes using Raman amplifiers to render at least a portion of the transmission medium lossless or better, effectively creating extra system margin, which can be utilized to offset losses associated with numerous interface devices.
Moreover, some aspects of this disclosure contemplate a metropolitan system utilizing numerous, possibly hundreds, of channels or more to facilitate efficient signal routing on a dedicated or semi-dedicated wavelength basis. That is, various network destinations may be associated with particular wavelengths, essentially creating dedicated links by allocating particular wavelengths to particular network nodes. In such a system, the number of channels used will increase dramatically compared to conventional systems. Amplifier technologies, such as Erbium doped amplifiers, are currently ill equipped to process the number of wavelengths that will be needed. This disclosure seeks to leverage the wavelength agnostic nature of Raman amplifiers to provide wide bandwidth operation, capable of amplifying many channels in a metro-optic network.
Still other aspects of this disclosure recognize that dispersion compensation can be provided for the metropolitan network using a Raman amplifier having a dispersion compensating fiber that serves as at least a portion of its gain medium. In that case, a single element can serve as both an amplification element, and a dispersion compensating element.
Other technical advantages may be readily ascertained by those skilled in the art from the following figures, description, and claims.